With reference to FIG. 1, a general vacuum system includes a vacuum pump 1 which has an inflow port, an outflow port, and an inhalation port for air, a cylindrical or box-like housing 2 which provides a surrounding space communicating with the inhalation port of the vacuum pump 1, a hollow manifold 4 which is connected to the housing 2 through an absorbing line 3, and plural vacuum pads 5 which are connected to the manifold 4. When compressed air flows at a high speed and is discharged through the vacuum pump 1, air inside each vacuum pad 5 is induced to the inhalation port and discharged along with the compressed air, and a negative pressure is generated inside each vacuum pad 5 at the same time. The generated negative pressure is used to hold a work object and to raise or move the work object.
If the surface of the work object is flat, the plural vacuum pads 5 are easily fixed at the same level. However, there occurs a problem in which the contact pose or the position of each vacuum pad 5 on the work object is not stable and the surface of the work object is damaged when all of the vacuum pads are flush with each other even in the case where a curved portion or a stepped portion is present on the surface. In order to solve this problem, a level compensator 6 is used in conjunction with the vacuum pads 5.
FIGS. 2 and 3 show an example of the level compensator according to a known technique. For convenience, the same reference numerals are given to functionally similar elements in both figures. The known level compensator includes a cylindrical fixing tube 7, a tube-shaped slider 8 which passes through the fixing tube 7 to perform up-and-down movement, and a spring 9 which is disposed between the fixing tube 7 and the slider 8 to elastically support the movement of the slider 8. A vacuum pad connected to the lower end of the slider 8 moves along with the slider 8, and thus the level of the vacuum pad is appropriately compensated in accordance with the state of the surface of a work object. The level compensator also serves as an impact absorber for absorbing impact occurring in the work object.
In a general vacuum system, in fact, the known level compensator is used as an apparatus for appropriately compensating the level of the vacuum pad in accordance with the state of the surface of the work object. However, the level compensator has problems in that the level compensator may have only limited uses, the system may become more complicated when using the level compensator, and an absorbing line may become longer when using the level compensator.